1. What would the pH of rain if the SO2 concentration is 0.3ppb and there is some ammonia to the atmosphere at a concentration of 0.015ppb ? Ammonia is ubiquitous in the environment, having both natural and anthropogenic sources. This is the last problem on the water chemistry notes (with changed concentrations - the first few lines of the solution are shown below. The equilibrium reaction for ammonia with water is NH3+H2ONH4++OH The equilibrium constant is known to have a pKb=4.74 at 25C. 2 Hence, [NH4+][OH]=104.74[NH3]